The present invention relates to an optical component connected to an array of optical fibers, and more specifically to an integrated optical component comprising N waveguides integrated into a glass substrate and respectively connected to the ends of N single-mode or multimode optical fibers. Even more specifically, the invention relates to such a component in which the fibers are glued to the substrate on the one hand at the fiber end that faces an output of the waveguide, on the other hand at a location distant from this output.
Such integrated optical components are known, for example in the French patent No. 2 612 301 filed 12 Mar. 1987 and assigned to Corning Glass Works. In accordance with the specifications of the preliminary specification T.A.NWT 000 442 published in November 1990 by Bellcore Laboratory (USA), such optical components must pass predetermined tests which assure in particular the mechanical strength of the fiber/substrate attachment and the good transmission quality of an optical signal. The mechanical strength is tested by a pulling force which is exerted upon the fiber/substrate attachment. This attachment must resist a force of 5N across the temperature range from -40.degree. C. to +85.degree. C., or in an atmosphere of 93% relative humidity at 60.degree. C., or further during aging for 2000 hours at 85.degree. C. Moreover, the signal loss observed for a transmitted optical signal must not exceed a predetermined threshold, for example 0.3 dB for a component with one input and two outputs.
An integrated optical component of the type described in the patent cited before, in which at least one waveguide integrated into a substrate is coupled at the output to an optical fiber which is attached to the substrate at this output and in a region separated therefrom, by at least first and second drops of adhesive product respectively, is described in the French patent application No. 91 03089 filed 14 Mar. 1991 by the applicant. The differential thermal expansions that could affect the optical continuity of the fiber/substrate combination as well as the mechanical strength of this combination are absorbed with an appropriate choice of the glass transition temperature of the two drops.
If it is attempted to apply the solutions described in the documents cited above to an integrated optical component connected to N parallel and adjacent optical fibers, difficulties are encountered as soon as N increases. It is the case for example, when one attempts to realize a component such as a 1.times.8 coupler, comprising at one end eight optical fibers connected in parallel--with a 350 .mu.m step for example--to eight aligned waveguide outputs formed in the component substrate. During the manufacture of such a component, the eight ends of the fibers are coaxially aligned, through suitable micromanipulations, with the eight waveguide outputs formed into the substrate, and are attached in these positions by eight drops of adhesive product with an optical quality insuring the optical continuity of the fibers and the waveguides. Following the design and process set forth in the documents cited above, the fibers are attached to the substrate upstream of these drops, by one drop of adhesive product spreading transversely across all the fibers in order to firmly attach them to the substrate.
If such a component is then submitted to the mechanical strength, temperature and humidity tests defined in the preliminary specification cited before, detachment of the glue drop deposited across the fibers can be observed, especially at the two transverse ends of it. It is clear that this phenomenon can very seriously affect the solidity of the fiber/substrate attachments at a point near the fiber/waveguide interfaces. Any disorder at this level can furthermore cause a harmful attenuation of the optical signals transmitted across the fiber/waveguide interfaces.
The present invention has therefore as its aim the manufacture of an optical component connected to an array of N adjacent optical fibers by adhesive means, and designed to avoid any detachment of the adhesive means used to attach the fiber to the substrate of the component, even with a great number N of fibers connected to the component.
This object of our invention, as well as others which will appear from the following description, are achieved by an optical component connected to a planar array of (N) adjacent optical fibers by adhesive means, these adhesive means comprising a plurality of drops of an adhesive product, each of them fixing between 1 and (N-1) adjacent fibers of the array to the component, each of these drops being non-contiguous to at least other of these drops, and at least one of the drops being axially and laterally offset with respect to at least one other drop of the plurality.
According to a preferred method of manufacturing the component in accordance with the present invention, transverse and longitudinal grooves are formed in the component to delimit the extension of each of said drops .